Re: [Qemu-devel] [RFC PATCH v2] Throttle-down guest when live migration does not converge.

[Eric Blake <eblake@redhat.com>]

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On 04/27/2013 02:50 PM, Chegu Vinod wrote:
> Busy enterprise workloads hosted on large sized VM's tend to dirty
> memory faster than the transfer rate achieved via live guest migration.
> Despite some good recent improvements (& using dedicated 10Gig NICs
> between hosts) the live migration does NOT converge.
> 

> 
> No exernal trigger is required (unlike option 1) and it can co-exist

s/exernal/external/

> with enhancements being pursued as part of Option 2 (e.g. RDMA).
> 
> Thanks to Juan and Paolo for their useful suggestions.
> 

> 
> ---
> 
> (qemu) info migrate
> capabilities: xbzrle: off auto-converge: on   <----

This part looks nice.

I'm not reviewing the entire patch (I'm not an expert on the internals
of migration), but just the interface:

> +++ b/qapi-schema.json
> @@ -599,10 +599,14 @@
>  #          This feature allows us to minimize migration traffic for certain work
>  #          loads, by sending compressed difference of the pages
>  #
> +# @auto-converge: Controls whether or not the we want the migration to
> +#          automaticially detect and force convergence by slowing

s/automaticially/automatically/

> +#          down the guest. Disabled by default.

Missing a (since 1.6) designation.

Also, use of first-person (us, we) in docs seems a bit unprofessional,
although you were copying pre-existing usage.  How about:

@xbzrle: Migration supports xbzrle (Xor Based Zero Run Length Encoding),
         which minimizes migration traffic for certain workloads by
         sending compressed differences of active pages

@auto-converge: Migration supports automatic throttling of guest
                activity to force convergence (since 1.6)

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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